Estimation of Nitrogen Fixed by Legumes in Long‐Term vs. Short‐Term Cropping Systems

Abstract

AbstractA critical evaluation of legumes should consider both the above‐and belowground contribution to N2 fixation. Based on the amount of N in crops and correcting for the changes of soil N as a result of cropping, 15 equations are presented for estimation of the apparent net amount of atmospheric N2 fixed by legumes grown in short‐ and long‐term cropping systems. In the final equation, all components of a legume‐cereal rotation system were considered. In estimating N2 fixation, including in the equation the non‐N2–fixing crop that follows the legume in the rotation is an innovation of the method, in addition to the system approach concept. The validity and accuracy of each equation in estimating N2 fixation by legumes is discussed. An example is provided using data from long‐term vetch‐barley (Vicia sativa L.‐Hordeum vulgare L.) rotation studies in Cyprus. The estimated amount of apparent net N2 fixation by vetch was 184 kg N ha−1, a quantity twice that usually estimated using only the aboveground vetch production. This result shows the importance of calculating apparent net N2 fixation by considering above‐ and belowground system components.